1. Technical Field
This invention relates to a plain bearing shell for a main crankshaft bearing.
2. Related Art
Familiar plain bearing shells of this kind feature a radial oil bore and an oil groove communicating with the oil bore, running in circumferential direction and in axial direction usually arranged centrally in the sliding surface or race on the inside face of the plain bearing shell. The oil is delivered under pressure to the main crankshaft bearing, passing through it to the oil bore in the oil groove in which, on the one hand, it distributes lubrication and cooling to the main bearing and from which it also is directed to the conrod bearing through a connecting bore in the crankshaft. To compensate installation tolerances, and therefore to ensure that this aperture of the oil line in the engine housing aligns with the oil bore in the plain bearing shell, the oil bore is in quite a few cases embodied as a slot.
The main crankshaft bearing comprises two semi-cylindrical plain bearing shells of which usually only the upper one features an oil groove of this kind. Both plain bearing shells have what are referred to as exposed surfaces at each of their circumferential ends. These are areas on the inside surface before the circumferential ends of both plain bearing shells, in which the plain surface is slightly recessed radially, helping to compensate for any inaccuracy in radial fit between two radial bearings combined to form a plain bearing shell. This radial expansion can however give rise to an increased level of lateral (axial) oil flow from the main bearing. This is undesirable because it reduces oil pressure and increases the need for oil, and this needs to be compensated by larger oil pumps.
Reference is always made to the bearing geometry with the stipulations of ‘in circumferential direction’, ‘axial’ and ‘radial.
To prevent this, in the more recent bearing shells of this type, the oil grooves frequently end in circumferential direction before the exposed surfaces. In this design, the oil grooves are machined into the plain bearing shell, usually with a milling operation, in such a way that their maximum depth is attained down their vertex, and usually extend continuously right to the ends in circumferential direction. Machining is generally performed on the shaped bearing shell.
Other known measures that counteract the axial outflow of oil may for example include an attempt to reduce bearing clearance, replacement of the exposed surfaces with deeper machining grooves or the vulcanization or insertion of elastomer rings to seal the bearing at its outer axial circumference. From a wide range of publications with this content, reference is made by way of example to DE 10 2005 009 470 A1, U.S. Pat. No. 6,491,438 B1 or DE 10 2005 011 372 A1. All named measures are fundamentally suitable for reducing the required volume of oil. All of these measures, including the partial grooves that terminate before the end point do however require more mechanical machining, which increases production costs.